JP 2008-32071 A (hereinafter referred to as “Document 1”) describes a thermal insulating member having thermal conductivity which is adjustable. The thermal conductivity of the thermal insulating member is adjusted by changing the internal pressure of a heat insulation container.
JP 2010-25511 A (hereinafter referred to as “Document 2”) describes a plate member having variable thermal conductivity. The plate member includes two thermally conductive members each having a plate shape and a mechanism for controlling the amount of gas which are disposed in a space enclosed in a casing, and the amount of the gas is controlled to change the thickness of the casing. In the case of the plate member, in a state in which the casing has a small thickness, the two thermally conductive members are in contact with each other, thereby forming a heat transfer path. In a state in which the casing has a large thickness, a space is provided between the two thermally conductive members, thereby shutting down the heat transfer path.